This entire series is on sale again on Steam, through the entire Steam Sale
However I'm quite confused by the pricing. X3: Albion Prelude is £4.99 while the X3 GoldBox package is £12.99 (Albion Prelude, Reunion and Terran Conflict). It was my understanding that Albion Prelude included everything that the prior games do so why would you buy the earlier ones too?
Even more oddly though the X-SuperBox (all 3 X3 games, X2 and two original X games) is just £9.99 so 3 pounds cheaper than the GoldBox. Bizarre. While the Egosoft Collection package containing all six plus X Rebirth and X Rebirth: The Teladi Outpost is also on sale if its not still a universal response of "meh" to this game.